Magnetic amplifier for reversible currents



April 18, 1950 FQRSSELL 2,504,675

MAGNETIC AMPLIFIER FOR REVERSIBLE CURRENTS Filed Aug. 21, 15947 Patented Apr. 18, 1950 MAGNETIC AMPLIFIER FOR REVERSIBLE CURBENTS Harry Forsseii, Ludvika, Sweden, assignor to Aliminna. Svenska Elektriska Aktiebolaget, Viaum, Sweden, a Swedish corporation Application August 21, 1941, Serial No. 769,977

In Sweden July 25, 1941 Section 1, Public Law 690, August s, 1946 Patent expires July 25, 196i 3 Claims. 1

Transductors, i. e. direct current magnetized 'inductances traversed 'by alternating current, have, as is well-known, obtained a vast use not only as separate amplifiers, but also as elements of regulators, in which latter case they usually have another function besides the amplifying one. In both cases, it has been found to be a limitation, that the transductor is in principle a non-po1ar-= ized element, as the amplified current traversing it is an alternating current, the strength of which is also independent of the direction of the resultant direct current magnetisation. A certain degree of polarisation can always be accomp ished by providing the transductor with a plurality of direct current windings, whether one of these is fed by an independent current or by the traversing alternating current after rectification. In the former case, the traversing alternating current will depend on either the sum or the difference between the ampereturns of the two currents supplied from outside, while in the latter case, the traversing alternating current always is kept near its minimum value when the selfmagnetisation and the external magnetisation oppose each other, but may rise to high values when they cooperate. Such a transductor, in which the value of the traversing alternating current has been made dependent on the direction of the independent direct current in either of the described manners or in still any other manner, is

referred to in the following lines as a polarized transductor. It is, however, desirable, in pure amplifyin connections as well as in connections for amplifying combined with another function, that the amplified current is a reproduction of the primarily influencing direct current as regards both magnitude and direct on, and the present invention refers to an arrangement for this purpose, the principal characteristic of which is that the rectified current from a polarized transductor is'confronted, at a pair of branching points, with a. comparison current of such value that the branched ofi' difference current changes its direction in dependence of the change of direction of a current influencing the polarized transductor.

According to a preferred form of the invention, the comparison current may also be derived from a transductor, and the latter may be symmetrical to the first-named transductor, so that two transductors polarized in opposite directions are ob tained, the difference current of which represents the amplification of the primary current flowing alternately in opposite directions.

Three forms of the invention are diagram-- matically illustrated in Figs. 1-3 of the accompanying drawing.

In Fig. l, i designates a pair of D. C. terminals through which the current of variable direction is introduced which it is intended to reproduce with an amplified power. 2 represents the A. C. terminals for introducing the. amplifying power. The latter terminals feed the A. C. winding of a transductor t and the primary winding of a transformer t, preferably through a reactor ii or other member for keeping the current constant. The terminals 8 feed a D. C. winding 8 on the transductor 3, while a polarizing winding l on the same transductor is fed in a manner further to be described. The alternating current from the transductor 3 is rectified in a rectifier 8 and the current from the transformer 4 in a rectiller 9. The two direct currents meet in a pair of branching-off points ID, from which the difference between them is led through a branch conduit containing a load ii. The direct current from the rectifier 9 passes, before the branching points, through the aforesaid polarisation winding 1, and moreover each of the two rectified currents passes through an ohmic resistance I2, I! respectively for producing a sufficient voltage between the branching points.

The arrangement now described operates in the following manner. A comparatively constant current is derived from the A. C. terminals through the transformer l and magnetizes the transductor 3 with a constant number of ampereturns, among other functions. The ampereturns from the winding 6 are added to or subtracted from the said constant number of ampereturns, depending on the direction of the current supplied through the terminals I. The alternating current and thus also the rectified current from the rectifier 8 willbe proportional to the resultant number of ampereturns. The difference between the said rectified current and the substantially constant direct current from the rectifier 9 traverses the branch conduit containing the load l3, and in choosing appropriate numbers of winding turns of the A. C. and D. C. windings on the transductor, this difference follows the difference between the total number of D. C. ampereturns of the transductor and the number of polarized ampereturns from the winding '11, i. e. follows the number of ampereturns of the winding 6 as regards magnitude as well as direction. In some cases it is not essential that the current in the branch circuit changes its sign exactly at the same time as the current in the winding 8, but it is on y essential that the former has the possibility of changing its direction in dependence of achange of direction of the latter.

In Fig. 2, the currents from two polarized transductors l4 and I! are compared. The A. C. windings of these transductors are fed from the A. C. terminals 2 through transformers l8, II. The [polarisation is due to the fact that the windings l9, l9 or the two transductors traversed by the independent direct current from the terminals i are connected over blocking valves 29, 2| so that each current direction can act only on one of the transductors. Each transductor is further provided with a self-fed winding .22, 29 respectively, which reinforces this action. If less accuracy is required, the seif-magnetisatlon alone may be sufllcient to accomplish polarisation. A good transductor, as a matter of fact, admits practically no alternating current when the external magnetisation and the self-magnetisation counteract each other. The currents from the A. C. windings of the two transductors rectified in the rectifiers 24, 25 respectively pass over counter voltage sources 26, 21 respectively to the two branching points 28, from which the differential current is branched off to the apparatus 29 intended to be influenced thereby. The voltage sources 26, 21 serve to create a suflicient voltage between the points 28 to overcome the ohmic re-" sistance in 29. In this case, the smaller one of the currents compared at the points 28 will be practically zero, so that the current from the temporarily active transductor essentially determines the amplified polarized current.

In Fig. 3, the A. C. terminals are still designated by 2 and the terminals for admitting the independent direct current of variable direction by I. The alternating current side feeds through transformers 9|, 32 the transductors 33, 34 and through transformers 35 a rectifier 35, the direct current from which feeds two polarisation windings 39, 40 on the transductors. The polarizing action of these windings is due to the fact that they, as compared with the windings 31, 38 connected to the terminals I, act magnetizing in opposite directions on the two transductors. The polarizing action is finally reinforced by the windings 4|, 42 traversed by the differential current. The rectifiers corresponding to the transductors are designated by 43, 44, resistances in the D. C. circuits by 45, 46, the branching points, from which the differential current is derived, by 41, and the load of the differential circuit by 48.

- .The manner of operation of this arrangement is substantially as fol'ows. One of the transductors is first magnetized by the sum of, the other by the difference between the ampereturns of the windings 31, 39 and 38, 40 respectively. Which one is magnetized by the sum or by the difference depends on the direction of the current through the terminals Leaving out so far the action of the windings 4!, 42, the alternating current of one transductor will be proportional to the sum of the polarisation current and the independent current, that of the other proportional to the difference between these. The difference between the two rectified currents, which traverses the load 48, therefore follows the current through the terminals l as regards magnitude as well as d rection. This difference also traverses the windings 4|, 42 which act in the same direction as the windings 31, 38, and thus reinforces the action of the latter windings. The D. C. windings of course should be so dimensioned that not even the total ampereturns of for instance the windings 39 and 4| can ever exceed the ampereturns of the winding lfl, which would cause a kind of reversed polarisation with a faulty function as a consequence.

The polarizing ampereturns of the windings 31, 38 cause among others the result that the current through the' resistances 45. 49 never can sink to zero, even if the external direct current sinks to zero. A voltage drop is therefore always obtained in these resistances, whereby the function of the connection is stabilized. In Fig. 2. on the contrary, it would hardly be suitable to replace the voltage sources 28, 21 by ohmic resistances, as the current traversing them could there sink to zero.

Although the transductors have been represented as single-phase in all the figures, they may of course also be polyphase. It is also possible to make them spare-connected in a manner known per se, so that for instance one D. C. winding is omitted on each transductor and the corresponding direct current introduced into the A. C. winding at points equipotential to the alternating current.

I claim as my invention:

1. Electric'current amplifying means, comprising a direct current saturable reactor, two saturating windings thereon, means for feeding a substantially constant current through one of said saturating windings, means for feeding a current to be amplified through the other of said saturating windings, a rectifier, the alternating current terminals of which are connected inseries with said reactor, and means for deriving :the difference between the direct current from saidrectifier and a substantially constant direct current. 2

2. Electric current amplifying means, compris-' sing a direct current saturable reactor, two saturating windings thereon, means for feeding a substantially constant current through one of said saturating windings, means for feeding a current to be amplified through the other of said saturating windings, a rectifier having its alternating current terminals connected in series with said reactor and its direct current terminals connected to two branching points in series with a resistance, a source of constant current connected to said branching points through a resistance; and a shunt winding connected between said branching points.

3. Electric current amplifying means, compris ing a direct current saturable reactor, two saturating windings thereon, means for feeding a sub-' stantially constant current through one of said saturating windings, means for feeding a current to be amplified through the other of said saturating windings, a rectifier having its alternating current terminals connected in series with said reactor, and means for deriving the difference between said substantially constant current and the current from the direct current terminals of said rectifier.

' HARRY FORSSELL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

